Method and Device for Intraoperative Determination of Drag Coefficient Values of Different Medical Instruments in the Use of a Medical Fluid Pump

ABSTRACT

Disclosed is a method for determining and controlling the internal body pressure during a medical procedure that includes controlling the output of a fluid pump by means of an estimated pressure value, wherein resistance coefficients ζ 1  and ζ 2  of a medical instrument required for the estimation of the pressure value are determined by evaluating a pressure behavior during pump start up.

CROSS-REFERENCE TO REFLATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/339,771, filed on Apr. 5, 2019, entitled METHOD AND DEVICE FORINTRAOPERATIVE DETERMINATION OF DRAG COEFFICIENT VALUES OF DIFFERENTMEDICAL INSTRUMENTS IN THE USE OF A MEDICAL FLUID PUMP, which is anational stage application based on PCT International Application No.PCT/DE2017/000332, filed on Oct. 5, 2017, claiming the benefit ofpriority to German Patent Application No. DE 10 2016 011819.9, theentire contents of each of these applications are hereby incorporated byreference.

FIELD

The present disclosure is directed to a method and device fordetermining the resistance coefficients in particular of different shaftand endoscope combinations when using a medical fluid pump, e.g. in thecontext of arthroscopy.

SUMMARY

In different medical interventions in the body's interior, fluids, e.g.gases or liquids are introduced into the body's interior and are removedtherefrom. An example here is arthroscopy, wherein, for example, in thecontext of an examination of the knee joint or a therapeutic treatment,the knee is irrigated with an irrigation fluid. Another exemplarytreatment is laparoscopy, wherein during a therapeutic intervention,gases (e.g. CO₂) are introduced into the body's interior. In the contextof these procedures, the measurement, the control and mainly thelimitation of the pressure in the body's interior is of particularimportance. For therapeutic interventions, it is in particular necessaryto secure a certain fluid flow, in order, for example, to wash smoke orblood out of the body's interior, simultaneously, however, to limit thepressure, in order not to damage the body tissue. For this purpose,different apparatuses and methods are available.

For avoiding most various drawbacks of prior methods, recently a methodand an apparatus directed thereto was presented that determines theinternal body pressure during the pump operation particularly precisely(WO 2015/144120), without a pressure sensor in the body cavity beingrequired. In this method, the data of a pressure sensor that is outsideof the respective body cavity, is used as a basis for an estimation ofthe pressure in the body's interior. For the estimation of the internalbody pressure, a mathematical model is used that describes the medicaloverall system consisting, e.g., of pressure controller, controllablepump motor, feed line, pressure sensor, medical feeding device (e.g.,shaft with endoscope), body cavity and, if applicable, fluid outlet(e.g., suction device) by a set of differential equations and combinesthem in a so-called state space model. Details are described in WO2015/144120.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 provides a representative graph of the pressure drop (Δp) overtime (t) and a representative graph of the flow (n1) over time (t);

FIG. 2 provides a plurality of characteristic curves for differentinstruments;

FIG. 3 illustrates an exemplary method to calculate ζ1 by means ofequation 4, wherein the loss term Δp has to be determined;

FIG. 4 provides a representative flow diagram for an exemplary methodaccording to the present disclosure;

FIG. 5 shows the data of an actual pressure measurement in a joint dummycompared to the estimated data of a system according to WO2015/144120;and

FIG. 6 shows the data of an actual pressure measurement in a joint dummycompared to the estimated data of a system according to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

As has been found during the operation of such a system, many of theestimation-critical parameters of the individual components describedabove are substantially constant. It has been found, however, that thedifferent medical feeding devices (e.g., the various possible shafts)exhibit very different parameters, in particular flow parameters.Depending on the used combination of shaft and endoscope (in thefollowing also: instrument), a very different pressure drop will occur.

For the operation of the medical liquid pump, therefore, beforebeginning an operation, the respective resistance coefficient (seebelow) has to be measured for each instrument. This can be made, forexample, such that in the context of an “open-flow measurement”, aliquid flow is generated and the pressure drop relative to the ambientpressure is measured. The measurement takes place, of course, outside ofthe joint. The obtained flow pressure corresponds to the instrumentpressure, i.e., the resistance coefficient of the underlying combinationof shaft and endoscope. The disadvantages of this measurementmethod-ology are obvious: The most important disadvantage of thismeasurement method is that with each change of instrument—i.e., in thecase of an intraoperative change of instrument—such a measurement has tobe carried out. Disadvantageous, herein, is in particular the requiredtime that is at least 15 to 30 seconds. Further, it is disadvantageousthat a certain amount of fluid has to be used for the measurement, whichcannot further be used. This requirement of time and fluid is onlydifficultly tolerated by the medical practitioners working with suchsystems.

When the pressure along the fluid flow between two specific systempoints is considered, then, with identical flow speeds and constantdensity, the relation-ship shown in equation 1 will result:

Δp=p ₁ −p ₂  Equation 1:

For instance, Δp describes the pressure drop across the used combinationof shaft and endoscope (the so-called instrument pressure) from thedifference of flow pressure in the hose and the stagnation pressure inthe joint. The stagnation pressure in the joint is the variable of thepump to be controlled and is not measured for the reasons mentionedabove. In order to determine the pressure in the joint, the instrumentpressure has to be measured, in addition to the measurable flowpressure. For this purpose, a characteristic curve can be determinedthat is based on the dimensionless resistance coefficients ζ1 and ζ2according to equation 2:

Δp=ζ ₁ ·n ₁ ²+ζ₂ n ₁  Equation 2:

By using equation 2 in equation 1 and re-arrangement with regard to p₂,the following statistical measurement equation 3 will follow:

({circumflex over ( )}p ₂)=p ₁−(ζ₁ ·n ₁2+ζ₂ ·n ₁)  Equation 3:

Herein, the left-hand side of equation ({circumflex over ( )}p₂)represents an estimation of the joint pressure. In order to determinethe resistance coefficients of equation 2, at least three pairs ofvalues (Δp) have to be recorded for three different flows (n₁). Such ameasurement is illustrated in FIG. 1. Herein, three different flows areadjusted, and the respective pressure differential is measured. As shownin FIG. 1, after a certain time, a stationary final value is obtained.The adjustment of the flow takes place by control of the motor speed ofthe pump. The determination of the pressure takes place in an open-flowmode, i.e., relative to the ambient pressure.

The methodology mentioned above has some disadvantages:

1) In order to obtain as precise resistance coefficients as possible, ithas to be waited, respectively, until the signal has reached thestationary final value.

2) For the identification of the resistance coefficients, at least threespeed ranges have to be started, otherwise there will be no solutionsfor the underlying system of equations.

3) Due to the required time for the adjustment of the stationary finalvalue in combination with the required speed ranges, a duration capableof being improved for the application of the instrument recognitionoutside of the joint will result.

4) The procedure is not suitable to carry out an identification of theinstrument (i.e., the determination of the instrument pressure) in thejoint. This would lead to too high an overpressure in the joint.

5) The fluid required for the measurement is not used for the operativemeasure.

It is the object of the present invention, therefore, to simplify themeasurement of the resistance coefficients for the differentinstruments. The measurement is to be faster and principally in the body(e.g., in the joint) and to consume as little fluid or gas as possible.

The solution of this object is achieved preferably by a method fordetermining and controlling the internal body pressure in medicalmethods,

wherein a fluid is pumped by a controllable pumping device through afeed line into a body cavity, wherein the feed line contains, at itspatient's end, an ex-changeable medical instrument, through which thefeed of the fluid into the body cavity takes place,

wherein the fluid can flow out of the body cavity through at least onesecond line,

wherein the pump included in the pumping device is controlled,

wherein at least the feed line contains a pressure sensor that measuresthe pressure in the line,

wherein the pressure measured by the pressure sensor is an inputvariable of a mathematical estimation system, which mathematicallydescribes a state space, which estimates the actual pressure in the bodycavity and controls the output of the pump by means of this estimatedvalue,

wherein the resistance coefficients ζ₁ and ζ₂ of the medical instrumentrequired for the estimation of the pressure are determined by that whenstarting the pump, the pressure behavior is evaluated for a certaintime, therefrom a characteristic curve is determined, and thecharacteristic curve is stored in a memory device of the pump.

The method according to the invention determines the resistancecoefficients ζ₁ and ζ₂ already at a one-time start of the pump withacceptable accuracy. A higher accuracy is achieved, when the starting iscarried out several times. As an optimum, the two-time start of the pumphas been found.

The term “starting the pump” comprises in particular the change of thepump output from 0 ml/min to a pump output adapted to the desiredinstrument and the intended use (e.g., 25 l/min for insufflation or 500ml/min for arthroscopy), e.g. by integrating a peristaltic roller pumpunder adjustment of a target speed. In special cases, the measurementcan also be carried out in a manner that the pump is changed from asmall output to a significantly larger output (e.g., from 2.5 l/min to25 l/min for insufflation or from 50 ml/min to 500 ml/min forarthroscopy). This is also included in the term “starting the pump”.Such an embodiment being less preferred requires the adaptation of thecalculations presented below, in particular of the calculation of thepressure loss term Δp.

The solution of the above object is achieved, further, preferably by amedical apparatus for supplying fluids into body cavities, including acontrollable fluid pump, a memory device, a feed line, a pressure sensorin the feed line, a medical instrument to be connected to the feed line,

Wherein the pressure measured by the pressure sensor is an inputvariable of a mathematical estimation system, which mathematicallydescribes a state space, which estimates the actual pressure in the bodycavity and controls the output of the pump by means of this estimatedvalue,

wherein the resistance coefficients ζ₁ and ζ₂ of the medical instrumentrequired for the estimation of the pressure are determined by that whenstarting the pump, the pressure behavior is evaluated for a certaintime, therefrom a characteristic curve is determined, and thecharacteristic curve is stored in a memory device of the pump.

In order to compensate for the disadvantages of the open-flow methodmentioned above, therefore, the following measurement approach issuggested:

For a given medical liquid pump, in a first test series, a plurality ofcharacteristic curves is recorded. For this purpose, the instrumentsprovided for the operation of the liquid pump (i.e., the combinations ofshaft and endoscope) are coupled to the pump, and the respectiveflow-dependent instrument pressure is measured and evaluated. The valuesmeasured for a certain instrument can be represented as a characteristiccurve. A plurality of characteristic curves that shows suchcharacteristic curves of different instruments, is exemplarilyillustrated in a simplified form in FIG. 2. It can be seen that thedifferent resistance characteristics of the instruments mainly depend onthe effective flow cross-section. It can be assumed that other physicaldependencies will behave in a time-invariant manner. As a result,different resistance coefficients (ζ_(1,z) and ζ_(2,z)) depending on theflow cross-section are obtained, wherein z is the number of recordedcharacteristic curves. From these characteristic curves, the ζ₂ valuesare stored in a memory device of the pump as a priori knowledge.

For measuring and storing the characteristic curves, different ways areconsidered. It is possible that, when manufacturing the pump, allapproved instruments are measured, and the resistance coefficients orthe characteristic curves are stored. In an-other embodiment, prior toeach application, i.e., after connecting the respective instrument tothe pump, a measurement and storage process of the resistancecoefficients or the characteristic curves is carried out. It is alsopossible, of course, that the pump is available on the market with somestored characteristic curves, but the user can also additionallymeasure, for his or her preferred instruments, the resistancecoefficients or the characteristic curves individually and store them inaddition to the already stored data.

In any case, before or during an operation, the measurement process cannewly be started, so that adaptations are intraoperatively possible.

In order to derive an algorithm for the instrument recognition in thebody (e.g., in the joint), the polynomial described in equation 2 ismodified as follows:

$\begin{matrix}{\zeta_{1} = {\frac{{\Delta\; p} - {\zeta_{2} \cdot n_{1}}}{n_{1}^{2}} = \frac{\left( {p_{1} - p_{2}} \right) - {\zeta_{2} \cdot n_{1}}}{n_{1}^{2}}}} & {{Equation}\mspace{14mu} 4}\end{matrix}$

Equation 4 describes the flow resistance ζ₁ as a function of themeasurable speed, of the measurable flow pressure p₁, of the notmeasurable stagnation pressure p₂ in the body and of a predeterminedvalue for the flow resistance ζ₂. The flow resistance ζ₂ is assumed asbeing constant within certain speed ranges. By a short, constant speedsupply, a suitable ζ₂ value is obtained by means of the pressure rise,said ζ₂ value being selected from the memory.

In order to be able to calculate ζ₁ by means of equation 4, the lossterm Δp has to be determined. This is described by means of FIG. 3:

For the calculation of the pressure loss term Δp, the followingconditions apply:

-   -   p₁=p₂ for n₁=0 in the time period (t₁−t₀) and t₃>0    -   p₁=Δp+P₂ for n₁>0

Under consideration of the mentioned conditions, at time t₂, themeasurable flow pressure can be deter-mined. The determination of thestagnation pressure p₂ takes place for times t≥t₃, after the dynamics ofthe measurement signal has dropped. The loss term results from thedifference (p₁−p₂).

It has to be taken into account that the accuracy of the calculation ofΔp depends on the amount of a potential leakage. In the case that thedetermined instrument parameters are outside of a plausible range, acharacteristic curve stored in the memory is selected.

A comparison of the method according to the invention to the prior artmethod described above shows the surprising advantages of the presentinvention:

-   -   The previous method (open-flow method) requires for determining        the resistance coefficients ζ₁ and ζ₂, the adjustment of three        different flows for the pump. In comparison, the method        according to the invention requires only a one- or two-time        start of the pump.    -   The prior art identification method takes 15 to 30 seconds,        whereas the method according to the invention (with a two-time        start of the pump) requires only about 7 seconds.    -   The prior art identification method has to be carried out        outside of the body. The identification method according to the        invention is, as a standard, carried out inside of the body, may        however also carried out outside of the body.    -   The prior art identification method requires time. The user has        to wait during the process, until he or she can begin with the        intervention. The method according to the invention is running        during the application in the back-ground, whereby the user is        not affected.    -   After the prior art identification method, the surgeon cannot        immediately begin with the intervention. For this purpose, he or        she has first to generate a certain fluid flow in the body's        interior (before distension). In the context of the method        according to the invention, the fluid flow produced for        identification is already used for predistension of the body        cavity, as a standard. The amount of un-used fluid is thus        minimized.

Overall there are, therefore, substantial advantages with regard to thespeed and the user friendliness. It is of particular importance that theaccuracy of the method according to the invention correspondsapproximately to the accuracy of the method known from prior art. FIG. 5shows the data of an actual pressure measurement in a joint dummy (shownin black) compared to the estimated data of a system according toWO2015/144120 (shown in gray). The actual values are never larger thanthe estimated values, usually they are slightly smaller than theestimated data, which is preferred for safety reasons. FIG. 6 shows thedata of an actual pressure measurement in a joint dummy (shown in black)compared to the estimated data of a system according to the invention(shown in gray). Here, too, the actual values are never larger than theestimated values, usually they are also slightly smaller than theestimated data, which is here, too, preferred for safety reasons. As aresult, an approximately comparable accuracy of the pressure estimationin the joint can be seen.

The present invention also relates to an apparatus for carrying-out themethod according to the invention, namely a medical fluid pump forirrigating body cavities (e.g., joint cavities). This may be a liquidpump, as well as an insufflator. A liquid pump that operates in the wayof a peristaltic roller pump is preferred according to the invention.The controlled pump supplies a fluid through a hose and a medicalinstrument, for example, a shaft with an optical system into a bodycavity, for example, a knee joint. The body cavity may comprise a devicefor discharge of liquid. The pump is operated, as intended, such that itgenerates an overpressure in the body cavity that widens (distends) thebody cavity. In the apparatus according to the invention, the internalbody pressure, as explained above, is determined by way of anestimation. A pressure sensor located outside of the body cavity in orat the hose determines pressure data that represent the input parameterfor an estimation. This mathematical estimation system describes a statespace, which estimates the actual pressure in the body cavity andcontrols, by means of this estimated value, the output of the pump. Suchan apparatus is described in WO 2015/144120. The apparatus according tothe invention includes, in addition to the pump described, an additionalmemory in which the results of the a priori knowledge are stored.

The memory device can be implemented in an unchangeable chip (e.g., anEPROM). Alternatively, of course, other, in particular exchangeable ormodifiable memory media can be considered. It may be provided that thememory device or the stored data can be modified by updates, forexample, by exchange of the memory device or by loading new data viacorresponding interfaces. Loading new data may optionally also be madevia the internet, wherein, of course, the safety of the loadingoperation has to be secured, in particular with regard to theauthenticity of the data source.

For determining the a priori knowledge of the characteristic curves, thepump manufacturer can, for ex-ample, measure all instruments providedfor the pump (i.e., all combinations of shaft and endoscope) and storethese measurement data in the memory device of every pump beforeshipping.

Alternatively and/or additionally, measurement data can be provided,wherein different instruments are simulated by a proportional valve.This is possible since, as explained above, the different resistancecharacteristics of the instruments mainly depend on the effective flowcross-section that can be simulated by different settings of aproportional valve.

Alternatively and/or additionally, the resistance coefficients ζ₁ and ζ₂provided by measurements of the instruments can be stored in the memorydevice of every pump. As soon as the pump is put in operation, the dataof the pressure sensor, i.e., the pressure obtained in the hose, arecompared to the stored characteristic values. Those resistancecoefficients with the largest possible match with the measurement dataare selected, and the resistance coefficients ζ₁ and ζ₂ are used in thecontext of the estimation system for the estimation of the body'sinternal pressure.

A potential sequence of the program is shown in FIG. 4.

The method according to the invention and the apparatus according to theinvention can be operated with different fluid discharge devices. It ispossible to secure the discharge from the body cavity through an opening(e.g., an incision) or a hose in a passive manner. It is also possibleto provide a pump that pumps the fluid out of the body cavity. Preferredare pump systems with two peristaltic hose pumps (double-roller pumps),of which one roller pump secures the inlet (conveyer pump) and the otherone secures the outlet (suction pump). The system according to theinvention also operates with several discharge systems.

The method according to the invention and the apparatus according to theinvention can be used in particular with liquid pumps in arthroscopy,urology, hysteroscopy, laparoscopy or for examinations of the backbone.Furthermore, insufflators can be operated by means of the methodaccording to the invention and the apparatus according to the invention.

An improvement of the apparatus according to the invention is that theresistance coefficients of every instrument are stored on the instrumentitself or can be determined by means of the latter. Thus, for example,it is conceivable to attach a transponder at every instrument, whichcontains data. By a corresponding transceiver at the pump, these datacan be read. The data of the instrument can immediately include theresistance coefficients. Alternatively, they may also be identificationdata, by means of which the resistance coefficients can be retrieved,e.g., from the pump manufacturer via the internet. Furthermore,alternatively, the data can also be stored on other media, e.g., onbarcodes that can be designed in a multi-dimensional manner, or magnetictapes.

What is claimed is:
 1. A method for determining and controlling theinternal body pressure during a medical procedure comprising the stepsof: pumping fluid using a pumping device through a feed line into a bodycavity, wherein the pumping device is controlled by a controller andwherein the feed line contains at a patient's end, an exchangeablemedical instrument through which the pumping of the fluid into the bodycavity takes place, providing a second line through which fluid can flowout of the body cavity, providing a pressure sensor and measuring apressure in the feed line using the pressure sensor, wherein thepressure measured by the pressure sensor is an input variable of amathematical estimation system, which mathematically describes a statespace, estimating the actual pressure in the body cavity using themathematical estimation system; and controlling the output of the pumpby means of the estimated value, wherein resistance coefficients ζ₁ andζ₂ of a medical instrument required for the estimation of the pressureare determined by that when starting the pump, a pressure behavior isevaluated for a certain time, therefrom a characteristic curve isdetermined, and the characteristic curve is stored in a memory device ofthe pump.
 2. The method of claim 1, further including the step of:determining the resistance coefficients ζ₁ and ζ₂ by starting thepumping device twice.
 3. The method of claim 1, wherein determining theresistance coefficients ζ1 and ζ2 of the medical instrument takes placepre- or intraoperatively.
 4. The method of claim 1, wherein themathematical estimation system is configured in the manner of a Kalmanfilter.
 5. The method of claim 1, wherein the fluid is a gas or aliquid.
 6. A medical apparatus for supplying fluids into body cavities,comprising: a controllable fluid pump for fluid into a body cavitythrough a feed line, a memory device, a pressure sensor for measuring apressure in the feed line, a medical instrument connected to a patientend of the feed line through which the pumping of the fluid into thebody cavity takes place, wherein the pressure measured by the pressuresensor is an input variable of a mathematical estimation system, whichmathematically describes a state space, which estimates an actualpressure in the body cavity and controls the output of the pump by meansof this estimated value, and wherein the resistance coefficients ζ₁ andζ₂ of the medical instrument required for the estimation of the pressureare determined by that when starting the pump, the pressure behavior isevaluated for a certain time, therefrom a characteristic curve isdetermined, and the characteristic curve is stored in the memory deviceof the pump.
 7. A medical apparatus for supplying fluids into bodycavities, comprising: a controllable fluid pump, a memory device, a feedline, a pressure sensor for measuring pressure in the feed line, and amedical instrument connected to the feed line at a patient end, whereinthe pressure measured by the pressure sensor is an input variable of amathematical estimation system, which mathematically describes a statespace, which estimates an actual pressure in a body cavity and controlsthe output of the pump by means of this estimated value, wherein theresistance coefficients ζ₁ and ζ₂ of the medical instrument required forthe estimation of the pressure are determined by that when starting thepump, a pressure behavior is evaluated for a certain time, therefrom acharacteristic curve is determined, and the characteristic curve isstored in the memory device which includes at least one microprocessor,at least one memory and at least one software.
 8. The medical apparatusof claim 7, wherein at least one memory contains data with theresistance coefficients of at least one instrument characteristic curve.9. The medical apparatus of claim 7, wherein the apparatus is aninsufflator.
 10. The medical apparatus of claim 7, wherein the apparatusis a liquid pump for arthroscopy, urology, hysteroscopy, laparoscopy, orfor examinations of the backbone.
 11. The medical apparatus of claim 7,wherein the apparatus is a liquid pump with integrated conveyer andsuction pump.